The present invention generally relates to a system of inner tubes for a pneumatic safety tire that comprises a primary annular inner tube made of flexible material and provided with a conventional inflation valve designed to pass through the wheel rim, and a set of secondary inner tubes made of an elastically extensible material circumferentially surrounding the inner tube and connected to the latter by at least one special valve (as disclosed in copending U.S. Pat. application Ser. No. 703,339, filed on July 8, 1976 now U.S. Pat. No. 4,054,169, issued Oct. 18, 1977, and assigned to Uniroyal S.A., also the assignee hereof, which application is hereby incorporated by reference herein).
The special valve can automatically open in the direction of inflation and likewise in the direction of deflation, the valve also being capable of automatically closing the moment the pressure in the set of secondary inner tubes drops below that prevailing in the primary annular inner tube.
The aforesaid secondary inner tube is made as a single enclosure or, preferably, as a plurality of elementary enclosures such as bags or small balloons each one of which is connected to the primary inner tube by means of a respective special valve of the aforesaid type.
This inner tube system makes it possible, in the event of a puncture, to maintain the pressure prevailing within the inner tube, thereby making it possible to continue to use and travel on said tire when the secondary inner tube completely deflates as a result of the puncture. This results because the pressure imbalance produced between the primary inner tube and the secondary inner tube causes each aforesaid special valve to close automatically.
The above design does not, however, make it possible to overcome a puncture or air leakage resulting from a minute perforation or an inadvertent excessive porosity in the material of the secondary chamber because the pressure drop or reduction in the secondary chamber is very slow, and the aforesaid special valve is not sufficiently responsive to detect the slow air leak and pressure differential between the two aforesaid inner tubes. Thus, the special valves will not automatically close.
The present invention makes it possible to remedy this inadequacy by preventing the gradual deflation of the primary inner tube in the event of a fine perforation in the secondary inner tube or upon an inadvertent excessive porosity in the secondary inner tube.